The veterinary studies area conducts epidemiologic investigations using data compiled by North American veterinary university teaching facilities, the Armed Forces Institute of Pathology, the Department of Defense Military Working Dog Agency, NCI's Registry of Experimental Cancers, and other sources when available. These investigations evaluate the role that environmental factors have in the etiology of cancer in animals, particularly to identify situations where the companion domestic animal may serve as a sentinel for human exposures to environmental carcinogens. Major areas of interest are necropsy findings among military working dogs who served in Vietnam 1968-1973 and died in the periods of 1968-1973 and 1974-1978; also household and lawn chemical exposures of pet dogs diagnosed with bladder cancer, and record linkage studies of West Virginian military veterans who served in Vietnam and elsewhere during the period of the Vietnam conflict. An earlier study of Vietnam service military working dogs, who died in Vietnam, found that they had a significant twofold excess of testicular seminoma. Also found was a similar excess among military working dogs that died in Okinawa. Further review of military health and service records now indicated that only military service in Vietnam is associated with the excess of seminoma. Among the 3,800 military dogs that were necropsied worldwide, 1968-1973, the only non-cryptorchid dogs under five years with seminoma were of Vietnam service. A study of prostatic disease among military working dogs finds a significant twofold excess of benign prostatic hyperplasia, beginning at age two, among those with Vietnam service. Another examination of the necropsy records shows a significant excess of cysts involving the congenital remnants of the branchial apparatus among Vietnam service military working dogs; similar excess, though not significant, is seen among West Virginians who served in Vietnam. A case-control study of 85 pet dogs with cancer of the lower urinary tract found significant associations with owner use of lawn insecticides and professional lawn care companies, and professional grooming plus exposure to flea and tick dips.